NO153612B - PROCEDURE FOR LUMPING MALT, NICKEL SULFID MATS. - Google Patents

Description

The invention relates to a method for leaching ground, nickel-containing sulphide mats which contain copper and iron.

It is known to leach nickel selectively from ground, nickel-containing sulphide mat containing copper, some iron and possibly some cobalt, and where the sulfur content is present in a non-stoichiometric amount in relation to the total amounts of metal present. According to a preferred and known method, a significant proportion of the nickel is thus leached from the mat by exposing the mat to atmospheric leaching in a sulfuric acid electrolyte at a temperature of up to approx. 100°C while aerating the solution. During aeration, the amount of iron in the solution is reduced by the iron being excreted as a precipitate of trivalent iron. Part of the copper is also precipitated.

In the patent literature, a large number of hydro-metallurgical processes are described for the selective leaching of nickel from nickel-containing sulphide mats, such as nickel sulphide and nickel/copper sulphide mats. As examples of patents in this technical area can be mentioned

US Patents No. 967072, No. 1756092, No. 2223239, No. 2239626 and No. 2753259. In the last three patents, the importance of using a mat is emphasized where the mat's sulfur content is less than the stoichiometrically necessary amount to react with the entire amount of metal present.

In an article entitled "Atmospheric Leaching of Matte at the Port Nickel Refinery" in the Canadian Mining and Metallurgical Bulletin (February, 1974) a detailed account is given

for atmospheric leaching of painted nickel-containing matte.

Granulated mat was used which contained little iron

(ca. 0.2% Fe), and the mat was ground to 99% -149µm with 50% -37µm. When using the mat with a low iron content, the leaching

times relatively short.

Later work regarding the atmospheric leaching of nickel-containing mat with a relatively high iron content showed that the presence of a high iron content, e.g. an iron content in the mat of up to approx. 20% by weight, increased the residence time for obtaining nickel solutions with a low content of both iron and copper, i.e. solutions containing less than 10 ppm of each of these metals, see US patent document no. 3962051. According to this patent document, the mat is granulated with a high iron content from a temperature that is at least 10°C higher than the liquidus/solidus temperature, by quenching the mat in water so that the mat will become more easily leachable after painting. According to this patent document, the measured mat is subjected to a first leaching step at atmospheric pressure to dissolve nickel selectively from the mat using a used copper electrolyte solution containing a sufficient amount of sulfuric acid to obtain a pH of up to approx. 2, while the solution is aerated until the pH of the solution during the leaching becomes 3.5-4.5, and the leaching in the first step is followed by a leaching in a second step under atmospheric pressure with the used copper electrolyte by using instead of air supply a suitable amount of a stronger oxidizing agents, such as oxygen, Mn04 -1 and S20g -2, to make the leaching at atmospheric pressure more complete as demonstrated by a rise in pH to above approx. 5, thereby forming a nickel solution with a low content of both iron and copper. The second oxidation step with a stronger oxidizing agent greatly shortens the residence time to end the leaching of the mat at atmospheric pressure.

The iron is separated more easily than the copper, and in order to ensure separation of the copper so that the desired low amount of copper remains, the residence time should be sufficient so that there will be an essentially complete separation of copper.

However, the use of strong oxidizing agents increased the costs of the process. There was also a tendency for the copper which had been separated from the solution to be oxidized and redissolved in the solution, especially when an excess of the stronger oxidizing agent was added. The ideal conditions for a rapid precipitation of iron were thus not always ideal for a rapid precipitation of copper. The increase in the length of stay for

obtaining a complete separation of copper also increased the costs as it had an adverse effect on the volumetric yield.

It would thus be desirable to provide a method which is sufficiently flexible so that relatively pure nickel leaching solutions with a low content of iron and copper can be produced with the help of this without it being necessary to simultaneously separate both iron and copper to the same remaining low content during the leaching, simultaneously with a maximum extraction of nickel as long as the main amount of the copper is separated.

It has been found according to the invention that this can be achieved by carrying out the leaching at atmospheric pressure to separate out the iron until the desired low amount of iron is left, then to complete the removal of copper from the nickel solution in a further step using a layer of ion exchange resin which is selective towards the absorption of copper, but not towards nickel and/or cobalt.

The invention thus aims to provide a method for leaching nickel-containing sulphide mat at atmospheric pressure, containing a relatively large amount of iron, in order to selectively and economically extract a significant proportion of the contained nickel with a low content of iron and copper.

The invention also aims to provide a leaching process for the selective extraction of nickel from nickel-containing mat, where the presence of iron and copper in the mat and/or the leaching solution and their adverse effect on the leaching can be counteracted by using a new combination of treatment steps to achieving a removal of essentially the entire amount of iron in an aeration step and removal of residual copper in another step.

The invention thus relates to a process by leaching ground, nickel-containing sulphide mat containing 20-75% by weight nickel, 5-50% by weight copper, over 0.5 and up to 20% by weight iron, possibly small amounts of cobalt, and sulfur in a non- stoichiometric amount of from over 4% by weight to 24% by weight, the sum of the content of nickel, copper and sulfur being at least 80% by weight, where the

painted mat is leached at atmospheric pressure in a spent copper electrolyte-sulfuric acid solution with a pH below 2 while vigorously aerating the solution, to selectively leach nickel

from the mat and produce an enriched nickel solution containing less than 10 ppm iron and copper in an amount above 5 ppm

and up to 750 ppm, so that a copper-nickel-containing sulphide residue remains, the enriched nickel solution is separated from the copper-nickel-containing sulphide residue, and the enriched nickel solution is brought into contact with a solid means for the selective uptake of dissolved copper from this while obtaining a purified nickel solution which is transferred for the extraction of nickel, while the copper is eluted from the

the roofing agent by passing a sulfuric acid solution through it with a pH below 2 to thereby form a copper sulfate-sulfuric acid electrolyte, the copper-nickel sulfide residue from the atmospheric leaching is subjected to high-pressure oxidation leaching with a sulfuric acid-containing solution at a temperature of 150-250<Q>C and a pressure of 15.0-64.3 kg/cm<2> thereby producing enriched copper sulfate-containing electrolyte and a leached residue which is removed, the enriched copper sulfate-containing electrolyte is subjected to electrolysis to extract copper from it and while forming a spent copper electrolyte with regenerated sulfuric acid, and the used copper electrolyte is re-circulated back to the leaching process for the painted mat, and the method is characterized by the fact that the enriched nickel solution obtained by separation from the copper-nickel holding sulfide residue, for selective absorption of dissolved copper is passed through an ion exchange resin layer which is selective for the absorption of dissolved copper and is selected from the group RN (CI ^COOH) 2 > RNH(C2H4NH)n and RC(NH2)NOH where R denotes polymers or copolymers of vinyl aromatic compounds, and n is an integer of 1 or greater, and the copper sulfate-sulfuric acid electrolyte obtained by elution of the copper from the absorp -tion agent, is used for the production of copper starting plate electrodes for use as cathodes in the electrolysis of copper from the enriched copper sulphate-containing electrolyte obtained by the high-pressure oxidation leaching of the copper-nickel sulphide residue.

The invention will be described more closely with reference to the drawings, of which

Fig. 1 shows a flow chart for carrying out the present method, Fig. 2 shows a group of curves each showing the aqueous copper concentration in the leaching liquid as a function of the leaching time and the degree of oxidation, and Fig. 3 shows a group of uptake curves showing the removal of copper using three different ion exchange resins.

According to the present method, the ground nickel-containing sulfide mat is leached at atmospheric pressure with a spent copper sulfate-sulfuric acid electrolyte with a pH below 2 while the solution is vigorously aerated, to selectively leach nickel from the mat and form an enriched nickel solution containing

keeps below 10 ppm iron and copper in an amount above 5 ppm and up to 750 ppm, so that a copper/nickel-containing sulphide residue remains, and the enriched nickel solution is separated from the residue and passed through an ion exchange layer which is selective for the absorption of copper, so that the copper is removed from the solution until there is copper left in it in an amount below 5 ppm, after which the nickel solution is used for the extraction of nickel.

In the above-mentioned method, long residence times during the leaching at atmospheric pressure are avoided as long as essentially all iron is excreted so that iron remains in an amount below 10 ppm. A special pre-treatment of the mat is not necessary, and it is not of decisive importance how the mat is granulated from the molten state. Strong oxidizing agents do not need to be used as long as the aeration is carried out for a sufficient time so that essentially all iron will be separated from the solution, even if up to 3oo, 500 or 750 ppm of copper is left in solution

the solution.

After the iron has been separated as a precipitate of trivalent iron (e.g. trivalent iron hydroxide and/or hydrated oxide of trivalent iron), the enriched nickel solution containing the residual amount of copper (. above 5 ppm) is filtered and then passed through a suitable ion exchange layer which is selective to the removal of copper, and essentially the entire amount of copper is removed from this solution.

By avoiding a long leaching time to separate out the entire amount of copper in the leaching solution, the subsequent removal of copper by means of ion exchange enables utilization of almost 100% of the capacity of the leaching circuit for the oxidation of iron. In this connection, a number of aerated leaching tanks can be used to carry out the leaching of the selected mat at atmospheric pressure, where the iron is separated together with the main amount of the copper.

Ion exchange as such is a well-known technique for selective

to remove ions from solutions. Thus, it is suggested e.g. in US Patent No. 283763 to use this method to pre-treat relatively dilute aqueous solutions of metals in order to concentrate the metal content in the solution for later reduction in an autoclave thereof. In this patent document, however, a metal that has been leached from an ore constitutes the main sought-after raw material, and not a by-product or a contaminant. In addition, this proposed recovery process uses reduction in an autoclave at elevated temperatures and superatmospheric pressure, which are not necessary for carrying out the present method.

When carrying out the leaching steps at atmospheric pressure, recycled used copper electrolyte is used as leaching solution. In the present method, the granulated is added

and painted mat with a high iron content together with used electro-

listen preferably.continuously to the first of a series of thoughts with agitation. The percentage of solids in the slurry is preferably kept at 10-20% by weight, and the slurry is vigorously aerated, preferably with air that is dispersed by means of a simple radial turbine rotating near the bottom of the tank. The system is operated at atmospheric pressure (ie an open system), but with a tank of sufficient depth, e.g. a depth of 4.5-6.1 m, to get

a sufficient partial pressure for oxygen around the turbine to satisfy the requirements for a rapid oxidation of the iron.

Oxygen-enriched air or pure oxygen can be used instead of air, but this is not recommended for economic reasons. The main purpose of the invention is to avoid the costs of strong oxidizing agents, but still to maintain a reasonable residence time when leaching at atmospheric pressure. In the present method, fast reaction rates are obtained without treatment in an autoclave. There is also no need for a precise temperature control during the granulation of the mat or for a pre-treatment with acid before the leaching to remove iron, as described in US Patent No. 3962051.

The more effectively the spent electrolyte is aerated, the faster the iron will be excreted. An increased partial pressure for the oxygen when using oxygen will also improve the excretion rate for the iron. This is clear from the following table:

The above experiments were carried out in a 1 liter open flask at 75°C and 21% solids using ungranulated mat with an analytical content (by weight) of 4.3% Fe, 39.6% Ni, 28.4% Cu and 22.8% S. The electrolyte used had an analytical content of 22 g Cu per litre, 31 g Ni per liter and 46 g H2S04

per litres.

Copper in aqueous solution behaves in a more complex way than iron. Up to a certain partial pressure for oxygen, strong aeration is beneficial. Above this partial pressure, the copper will first precipitate and then redissolve. In fig. 2 shows this effect when treating the above-mentioned mat under conditions described in the above section.

Example (Percentages by weight)

A mat containing 4.3% Fe, 39.6% Ni, 28.4% Cu and 22.8% S and had been ground to pass through a 74 µm mesh screen. while at least 50% passed through a sieve with a 52 µm mesh opening (slurried with process water with a solids content

hold of 40%) , treated with a used electrolyte with an analytical content of 31 g Cu per litre, 70 g Ni per liter and 64 g H2S04 per litres, and is processed further in accordance with that in fig. 1 showed flow chart. Used electrolyte and mat slurry are thus added to the first tank of a series of successively arranged leaching tanks (e.g. 5 tanks each of 56,780 litres), so that the percentage content of solids in the first tank is approx. 15%. The temperature in the leaching tank is kept at 70-75°C, and each tank is ventilated from the bottom of the tank. For slurry at a depth of

4.6 m, the air pressure at the outlet of the gas introduction line will thus correspond to a partial pressure for oxygen of approx. 0.3 atmosphere.

According to fig. 1, the mat is essentially leached at atmospheric pressure in the tank 10 for approx. 6 hours, during which time nickel is selectively dissolved and iron is excreted to a residual content of less than 5 ppm, and the analytical copper content is approx. 40 ppm. The enriched solution has an analytical content of approx. 65 g Ni per liter and a pH of 5-5.5.

The enriched solution and sulphide residue are transferred for solid-liquid separation at 11, the solids being transferred to autoclave 12 for pressure oxidation with water and spent copper electrolyte as shown, while the nickel solution with a low iron content is transferred to the ion exchange layer in column 13, in which the 40 ppm copper in the solution is selectively absorbed by the ion exchange resin in 13 and the copper content in the solution is reduced to below 5 ppm. The nickel solution or liquid 14, which also contains some cobalt and which leaves the ion exchange layer 13, is transferred for nickel-cobalt recovery.

The copper in the resin layer is removed by means of the recycling solution 15A from the copper starter plate tank 16, to which the solution 15 from the ion exchange layer 13 is added for the production of copper starter plate electrodes using titanium as the cathode from which the deposited starter plate can be removed, and using lead as an insoluble anode . The copper starting plate electrodes 16a are later transferred to the electro-extraction tank 17 for copper and are used to supply a part of the starting cathodes which are necessary for the extraction of copper from the high-pressure leaching solution after pressure leaching of the sulphide residue in the autoclave 12, in which the residue is mixed with used electrolyte which is supplied at 12a with a solids content of approx. 20% by weight, the pressure leaching being carried out in the presence of air at a pressure of approx. 42 kg/cm<2> excess pressure and a temperature of approx. 180°C

for about. 0.5 hour while adding sufficient sulfuric acid to maintain a pH of approx. 2 in the drain from the autoclave.

After the pressure leaching, the charge is transferred for liquid-solid separation at 18, and the remainder is taken care of at 19, and the separated liquid solution is transferred for electroextraction of copper at 17 for the extraction of copper. The solution has an analytical content of approx. 70 g Ni per liter and 60 g Cu per liter and a pH of approx. 2.

As the copper is deposited on the starter plates, a spent copper electrolyte 17a is formed which is recycled as shown for atmospheric leaching at 10 and for pressure oxidation leaching at 12.

As mentioned above, the ion exchange layer used is selective towards the absorption of copper. After the ion exchange layer has reached a constant state in terms of copper concentration, the acid regenerated at 16 is recycled as spent acid 15A to the ion exchange layer 13 to remove the absorbed copper and regenerate the resin pix.

The ion exchange resins which have been found to be useful for carrying out the present process are as follows:

The groups R denote polymeric resin structures and n an integer of 1 or more. The preferred polymer resins include polymers and copolymers of vinyl aromatic compounds. Examples of such resins are polystyrene and a copolymer of polystyrene and divinylbenzene.

The breakthrough uptake curves for the above ion exchange resins are shown in fig. 3. The resin CS-346 is particularly advantageous because it has the highest absorption capacity as its absorption curve lies furthest to the right. The data is based on residence times of approx. 14 minutes at a temperature of approx. 23°C. The treated amount of solution is indicated in multiples of layer volume, e.g. 200, 400,

600 etc.

With a 2 N H-jSO^ solution, the copper can be easily removed from the resins. Other ion exchange resins which are selective for copper can be used. The sulfuric acid solution used to remove the copper from the ion exchange resin can usually have a concentration within the range 0.5-10 N.

When carrying out the high-pressure leaching of the copper-nickel sulphide residue, the supplied slurry can have a solids content of 10-40%, and the sulfuric acid is added in a sufficient amount so that the drained slurry will have a pH of approx. 2. The slurry is leached with oxidation at an elevated temperature of 150-250°C, preferably 175-200°C and an elevated pressure of 15.0-64.3 kg/cm* for 0.75-3 hours to form an enriched solution containing copper and nickel and which is transferred to the tank for the electroextraction of copper.

After the high-pressure leaching of the sulphide residue from the leaching at atmospheric pressure, the enriched solution usually contains 60-90 g Ni per liter and 4 0-7 0 g Cu per litres.

After the electroreduction, the used electrolyte can contain 60-90 g of Ni per litre, 20 - 40 g Cu per liter and 10 - 90 g HoS0, per litres.

2 4

The electroextraction of copper is well known and will not be explained in more detail here.

Claims (1)

Process for leaching ground, nickel-containing sulphide mat containing 20-75% by weight nickel, 5-50% by weight copper, over 0.5 and up to 20% by weight iron, possibly small amounts of cobalt, and sulfur in a non-stoichiometric amount of from over 4% by weight to 24% by weight, the sum of the content of nickel, copper and sulfur being at least 80% by weight, where the painted mat is leached at atmospheric pressure in a used copper electrolyte-sulphuric acid solution with a pH below 2 while the solution is vigorously aerated, for selective to leach nickel from the mat and produce an enriched nickel solution containing less than 10 ppm iron and copper in an amount above 5 ppm and up to 750 ppm, so that a copper-nickel-containing sulphide residue remains, the enriched nickel solution is separated from the copper-nickel-containing sulphide residue, and the enriched nickel solution is brought into contact with a solid agent for the selective uptake of dissolved copper from this to obtain a purified nickel solution which is transferred for the extraction of nickel, while copper ret is eluted from the recording agent by passing a sulfuric acid solution through it with a pH below 2 to thereby form a copper sulfate-sulfuric acid electrolyte, the copper-nickel sulfide residue from the atmospheric leaching is subjected to high-pressure oxidation leaching with a sulfuric acid-containing solution at a temperature of 150-250 °C and a pressure of 15.0-64.3 kg/cm<2> to thereby produce enriched copper sulfate-containing electrolyte and a leached residue which is removed, the enriched copper sulfate-containing electrolyte is subjected to electrolysis to extract copper from it and while forming a spent copper electrolyte with regenerated sulfuric acid, and the spent copper electrolyte is recycled back to the leaching process for the painted mat, characterized in that the enriched nickel solution obtained by separation from the copper-nickel containing sulphide residue, for selective absorption of dissolved copper is passed through an ion exchange resin layer which is selective for absorption of dissolved copper and is selected from the group RN (Cf^C OOH) 2, RNH(C2H4NH)n and RC(NH2)NOH in which R denotes polymers or copolymers of vinyl aromatic compounds, and n is an integer of 1 or greater, and the copper sulfate-sulfuric acid electrolyte obtained by elution of the copper from the absorp- sion agent, is used for the production of copper starting plate electrodes for use as cathodes in the electrolysis of copper from the enriched copper sulphate-containing electrolyte obtained by the high-pressure oxidation leaching of the copper-nickel sulphide residue.